656 
PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA 
Ȃ 
where A, B, C are constant which stand for the initial condi- 
tions, namely 
A=a,(t-0) X,(t- 6), 
B = a,;(t = 6) W, 
C=a, (t-0) W. 
The economic meaning of (V.13), (V.14) at a given point of 
time has been discussed already on the occasion of our short- 
run analysis of chapter II (sections 5 and 6), and there is no 
need for repetition here. But besides the determination of quan- 
tities and prices at a given point of time, the (V.13), (V.14) 
now bring out their movements through time as well. 
As can be seen, each physical quantity follows a time-path 
of its own in time, expanding at a particular rate (g+7;) which 
is the sum of two rates of increase: the rate of growth of po- 
pulation and the rate of change of per-capita demand. The first 
of these two rates is the same for all goods, but the second is 
different from one commodity to another. Therefore, unless 
per-capita demand remains constant in time (i.e. unless there 
is no technical progress) the whole production structure in phy- 
sical terms is changing as time goes on. This means that, while 
growing, the system is continually changing the proportions in 
which it produces the various commodities. 
The (V.14) show moreover that each relative price is also 
changing in time in its own way. With the convention of adopt- 
ing W, the wage rate, as numeraire, each price is decreasing at 
a rate resulting from a weighted average of the pace at which 
technical progress is going on in the sector to which it refers, 
and in the sector which produces capital goods for it. Since 
all these rates are also different from one another, the whole 
price structure is changing as time goes on 
101 Pasinetti - pag. 86